Hard surface modeling - Knife
The Subdivision Surface modifier (which it looks like you are using) smoothes the object based on the average of the points. So in order to make a crease look sharper, add more geometry there. You can do this with a loop cut by using CtrlR. There are also many other ways.

But then again, as mentioned by @RobinBetts, it is much easier to make the handle and blade separately, apply the modifiers, and then join them together.